The present invention relates to internal combustion engines, and more particularly, to regulating the pressure within crankcases of internal combustion engines.
Controlling oil consumption in a ported two-stroke diesel engine is often difficult. First, openings in cylinder walls of the engine for exhaust discharge and air intake provide paths where oil can be introduced into the exhaust discharge or the intake plenum. Accordingly, oil can be burned and consumed as the oil-contaminated intake air is drawn into the cylinders or oil can be released as unburned hydrocarbons with the exhaust. Piston ring packs are designed to minimize such oil consumption.
For example, in one design, oil control piston rings do not cross either the intake or exhaust ports while the compression rings do cross the intake and exhaust ports. This design separates the oil control and compression rings on the piston such that there is a large piston skirt area that has limited lubrication during engine operation. Accordingly, engine designers must balance the design of the oil control rings to allow sufficient oil on the piston skirt and compression rings to properly lubricate these areas and yet minimize oil in these areas to control oil consumption and reduce the emission of unburned hydrocarbons.
Proper design of the oil control rings to provide the correct amount of oil is difficult due to the dynamic nature of the pressure in the engine manifold and crankcase. During high power operation of the engine the crankcase pressure is typically lower than the intake manifold pressure, which forces oil toward the crankcase. If the oil control rings are too aggressive in removing oil the compression rings and piston skirt can become too dry (oil starved) and fail. During engine idle and low power operation, the crankcase pressure is often higher than the intake pressure, forcing oil toward the combustion chamber and exhaust and intake ports.